4;o 



NA TURE 



[March 19, 1903 



the region surveyed in i his way is the province of Westphalia, 

 including Waldeck, Schaumburg-Lippe, Lippe-Detmold and 

 the neighbourhood of Rinteln. The chart, which is pub- 

 lished by Messrs. Dietrich Reimer in Berlin, contains, be- 

 sides tables, an explanatory text describing much useful 

 information concerning the monthly and yearly rainfalls 

 of the various districts. The mean values employed are 

 those that have been determined from a reduction of observ- 

 ations extending over the ten years 1892-1901, and 201 

 stations have been included in the discussion. Although 

 the period of ten years is rather short for some purposes of 

 deduction, when it is considered that there is a secular 

 variation of rainfall of about thirty-five years, yet Prof. 

 Hellmann, gives some interesting figures in respect to the 

 variation of rainfall in this decade. Thus he says that for 

 all practical purposes it can be assumed that in the province 

 of Westphalia the yearly fall varies between 134 and 66 

 per cent, of the mean value, or that during the wettest year 

 twice as much rain fell as in the driest year. From tin- 

 statistics of two stations, as Giitersloh and Arnsberg, ex- 

 tending from 1836 and 1866 respectively, the wettest years 

 were 1841, 1843, 1X07, 1SS0, 1882 for the former, and 1867, 

 1880, 1882, 1895, 1898 for the latter. The driest years for 

 the two places were 1*47, 1S57, 1865, 1874, 18S5, and 1874, 

 1SS7, 1892 respectively. 



Two simple lecture experiments described by Dr. Gar- 

 basso, of Turin, in the Nuovo Cimento are worthy of notice. 

 One consists in arranging three Bunsen coils, of E.M.F. 

 1 '8 volts and internal resistance o'i ohms, successively in 

 series and in parallel, first with a wire of resistance o'oog 

 ohms, and secondly with a lamp of resistance 10 ohms. A 

 calculation of the currents produced in the four cases is 

 confirmed by the experimental result that the wire glows 

 when the cells are in parallel but not when they are in 

 series, while the lamp glows when they are in series but not 

 when they are in parallel. The second experiment consists 

 in showing the dynamical action between unlike parallel 

 elements of the same current by means of a so-called " plane 

 spiral," which consists of a wire bent so as to form branches 

 alternately to the right and left, separated by vertical por- 

 tions. When a current is passed through the wire the 

 " spiral " becomes elongated, and that this effect is not due 

 tD heating is shown by breaking the current; if the latter 

 has been of short duration, the spiral will resume its previous 

 length. The spirals of Roget utilised by R6iti in his in- 

 terrupter show the attractive force between elements of like 

 parallel currents ; in the present case the current elements 

 are unlike, and they repel each other. 



Considerable uncertainty lias in the past prevailed re- 

 garding the limits of combustibility of different flames as 

 measured by the percentage of carbon dioxide and other 

 combustion products at the instant when extinction occurs. 

 Different writers have given numbers varying from vy per 

 cent, of carbon dioxide for a small petroleum lamp up to 

 14 or even 25 per cent, for a candle. A series of experiments 

 described by MM. L. Pelet and P. Jomini in the Moniteur 

 scientifique tends to throw light on the question. The com- 

 bustible was in ever} 1 ase burnt in a bell glass, and the 

 gases remaining analysed after extinction. The general 

 conclusion is that the limit of combustibility is not always 

 the same for the same substance. It depends (a) on the 

 nature of the substance, (b) on the temperature of the flame, 

 (c) on the quantity of combustible gas introduced into the 

 flame per unit of time, and (J) on the temperature of the 

 surrounding air. The first three factors, however, are de- 

 pendent to a large extent on each other, especially for liquid 

 NO. 1742, VOL. 67] 



and solid combustibles, and it results that the chemical 

 equilibrium between the combustibles, the oxygen and the 

 products of combustion is a function of the temperatures 

 alone. A practical application of the results to bath-heaters 

 is considered. 



An article on the " Common Basis of the Theories of 

 Microscopic Vision," contributed to the Zeitschriftfur wissen- 

 ichaftliche Miorosiopie by Mr. Julius Rheinberg, has been 

 translated by the author and published in pamphlet form. 

 The method of formation of an image by a microscope 

 objective is considered in detail, from the point of view 

 of the wave theory of light, By the use of carefully drawn 

 diagrams, mathematical analysis is entirely dispensed with, 

 while yet clear quantitative results are obtained. The general 

 effect of a lens in altering the curvature of light waves pass- 

 ing through it is now generally known, but the conditions 

 determining the resolving power of a lens might be 

 popularised with advantage, and the pamphlet before us is 

 well adapted to this end. Even those possessing the know- 

 ledge requisite to pursue the mathematical investigation of 

 the subject will find it interesting and profitable to follow 

 the author in his lucid and painstaking effort to obtain an 

 explanation directly from first principles. Several repro- 

 ductions of photographs are given, and these render the 

 argument more effective. Those unacquainted with the 

 wave theory will be surprised to find that, on looking 

 through a microscope at a number of lines ruled on glass, 

 it is possible, under suitable conditions, to see more lines 

 than are actually in existence ; so far from being true is the 

 old adage that " seeing is believing." 



We have received two parts of the Nat. Hist. Trans. 

 of Northumberland, Durham and Newcastle. In the one (vol. 

 xii. part ii.) Mr. J. E. Robson completes the first volume 

 of his catalogue of the Lepidoptera of the district. The 

 second (xiv. part i.) includes a report on dredging and other 

 marine researches undertaken by the Society in 190 1. ll 

 is suggested that some of the flagellate infusorians met 

 with in parts of the North Sea where there is no plankton 

 may subsist on dissolved salts, like algas, and thus form 

 the means whereby inorganic are converted into organic- 

 substances. This account is supplemented by the report on 

 the scientific investigations carried out during 1902 under the 

 direction of the Northumberland Sea Fisheries Committee. 

 As regards fishing, the committee has to record an un- 

 usually successful season, and it gives an elaborate return 

 of the number of marketable fishes captured. The report 

 includes an account of the structural changes which take 

 place in the common crab during the shedding of its shell, 

 and likewise a description of its normal growth. 



Prof. Grenville Cole has contributed to a work en- 

 titled " Ireland : Industrial and Agricultural " an interest- 

 ing sketch of the topography and geology of the country, 

 and an account of Irish minerals and building stones. 



In a report upon the present condition of Rhodesia, pre- 

 sented to the Directors of the British South Africa Company 

 (1903), Mr. J. F. Jones, C.M.G., expresses a sanguine 

 opinion about the future of the country. There appears to 

 be plenty of good coal, the auriferous deposits are of a 

 " highlv payable nature," while the " copper, zinc and lead 

 deposits promise to rank among the richest in the world." 



Dr. A. von Krafft describes the " Exotic Blocks " of 

 Malla Johar in the Bhot Mahals of Kumaon (Mem. Geoi; 

 Surv. India, vol. xxxii. part iii., 1902). These blocks he 

 attributes to vulcanic outbursts, they being fragments torn 

 from rocks in situ, through which the volcanic material 



